1. Field of the Invention
The present invention relates to an apparatus and method for measuring transmission property of a CDMA (code division multiple access) base station, and more particularly, to an apparatus and method for measuring output power of a pilot channel at the CDMA base station.
2. Description of the Prior Art
In general, CDMA (code division multiple access) refers to a kind of multiple access method, which allows a plurality of users to communicate with each other at the same time and/or frequency in a wireless communication system employed in car phones, cellular (or portable) phones and so forth.
The CDMA system is a spread spectrum communication system, in which information signals are transmitted in a state in which the information signals are subjected to spreading at a wider bandwidth than that of the original information signals. Further, when original data are transmitted, they are subjected to spreading by means of PN (pseudo random noise) codes called spreading codes. Then, when the spread data are received, they are subjected to de-spreading by means of the same PN codes as the PN codes which are used to transmit the spread data, so that the de-spread data are regenerated into the original data. In this CDMA system, there is a near-far problem. This near-far problem is generated in a case, in which, a desired mobile station is far from a shared base station, while an undesired mobile station is near the shared base station. To be more specific, the more distant desired mobile station receives weaker signals than interference signals due to interference with the less distant undesired mobile station in spite of de-spreading, so that it is impossible for the desired mobile station to perform demodulation. Consequently, the more distant desired mobile station has difficulty in performing communication due to such interference. In order to solve the near-far problem, it is necessary to precisely control the transmission power in such a manner that the less distant mobile station is operated with a lower transmission power, but the more distant mobile station is operated with a higher transmission power.
Meanwhile, communication between a base station and at least one mobile station within the base station is performed through forward and reverse links, in which the forward links are to transmit signals from the base station to the mobile station, while the reverse links are to transmit signals from the mobile station to the base station.
Further, each forward link established from the base station to the mobile station is made up of three types of overhead channels, i.e., a pilot channel, a synchronous channel and a paging channel in an idle state, but it is made up of four types of channels, including another type of overhead channel, i.e., a traffic channel in a busy state.
Therefore, the total transmission output power of the base station encounters a rapid change according to various parameters related to the traffic channels. For this reason, it is difficult to measure accurate transmission output power. In order to solve this problem as well as accurately measure property and error of the transmission output power of the base station, either output power of the pilot, synchronous and paging channels, or output power of only the pilot channel should be measured except for output power of the traffic channels as a dynamic parameter.
However, there is a problem in that it is difficult to measure transmission output power of only the pilot channel among the pilot, synchronous, paging and traffic channels, which are received in mixture with one another in the same frequency band.